1. Field of the Invention
The present invention relates to duplexers and, in particular, to a duplexer for use in a mobile telephone system, for example.
2. Description of the Related Art
A duplexer for separating transmission and reception signals in a mobile radio wave band is disclosed in Japanese Unexamined Patent Application Publication No. 2008-504756. As illustrated in a circuit diagram of FIG. 7, the disclosed duplexer includes a receiving filter 1, arranged in a reception path RX, which operates using a surface acoustic wave (SAW) and a transmitting filter 2, arranged in a transmission path TX, which operates using a bulk acoustic wave (BAW).
Since a BAW piezoelectric resonator, which is inferior to a SAW resonator in secondary non-linear characteristics, is used in the transmitting filter of the duplexer, a significant amount of intermodulation distortion (IMD) is generated.